The vortex interference to aerodynamic instability on the rectangular section with side ratio of B/D =4 (B : width length, D : height length) was experimentally investigated. The rotation axes were varied and a splitter plate was installed in the wake to destroy the Karman vortices. Two types of the interference phenomena were confirmed. One is the interference between motion-induced excitation and Karman vortex, the other is between torsional flutter instability and Karman vortex. The lock-in phenomenon of Karman vortex shedding to the body motion affected the vortex shedding from the leading edge and the unsteady pressure characteristics at trailing edge.

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Cables of cable-stayed bridges vibrate largely under wind and rain, and this vibration is called the rain-wind induced vibration. This vibration seems to be caused by the upper water rivulet formation on a cable surface, the axial flow in a near wake, and the 3-D vortex shedding along cable axis. However, the detail vibration mechanisms have not soled yet. In recent researches, they often explain that the moving water rivulet plays an important role on the vibration. Therefore, this study aims to measure aerodynamic derivatives under the moving rivulet condition and to clarify the role of the moving rivulet for the rain-wind induced vibration.

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This paper describes how the wake behind a circular cylinder as a splitter plate approaches the cylinder. Measurements were conducted in a water tank at Re=1.12×10⁴ based on the diameter of the cylinder. As the splitter plate was traversed horizontally at three levels from a far-off position, in an early stage the base suction increases gradually, but in fell critically at a certain position depending on the level. To make clear the mechanism of the critical change. PIV measurements were conducted for pre- and post-critical régime. It was found that the formation length changes in accordance with the variation of the base pressure

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Since flutter phenomenon is catastrophic oscillation, its stabilization is very important problem in the design of long span bridge girders. The flutter characteristics are discussed from the unsteady pressure distribution on bridge deck surface under heaving/torsional vibration. In this research wind tunnel tests are carried out for separated box girders with the triangle fairings and the vertical plate to improve flutter instability of long span bridge girders. The results shows attachment of the triangle fairings and the vertical plate is effective for reduction of the key aerodynamic derivative A₁^* and H₃^*. From the unsteady pressure measurement and flow field around the girders under the heaving/torsional 1DOF forced vibration, it is revealed that this is brought by the phase control by the installation of vertical plate.

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This study clarifies in a wind tunnel test the characteristics of wind forces on a diagonal bracing member in the wake of a column member of a steel latticed tower with members of circular cross-section. Furthermore, the wind responses of the bracing member are evaluated by using the wind forces in the modal analysis, and then compared with the responses obtained from the fullscale measurement. The surface of test model was roughened artificially by small circular section strings to improve local similarity with regard to Reynolds number to the full-scale measurements. When the entire bracing member is within the wake of the column, the fluctuating wind forces on are generated by the shedding vortex of the column. When only part of bracing is in the wake of the column, the fluctuating wind forces are composed of the components of the shedding vortex of the bracing member and the column. It is clarified that the evaluated wind responses of bracing member are in good agreement with the full-scale measurement values, and are mainly affected by the shedding vortex of the windward column.

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The rooftiles are lifted just before they are dislodged and scattered. It seems that the characteristics of wind pressure and force on these tiles might be different from those on tiles which are not lifted. In this study, the wind pressure and force acting on artificially lifted roof tiles were measured. The results show the following: 1) The mean wind force on rooftiles located near the middle of the roof and near the gable increase with the degree of lift at some wind angle of attack, depending on tile shape. 2) The internal pressure and external pressure on roof tiles change with the degree of lift and the change increases the peak force on the tiles. The tendency of increasing peak force depends on the wind angle of attack and the roof tile location. In the middle of the roof, the increasing peak force at the wind angle of attack along the ridge is mainly caused by the change of internal pressure. Near the gable, the increasing peak force at the wind incident on the corner is caused by the change of external pressure.

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Wind loads on free-standing canopy roofs have been investigated in a simulated turbulent boundary layer. Three types of roof geometries, i.e. gable, troughed and mono-sloped roofs, with roof pitches between 0°and 15°, were tested. Wind pressures were measured simultaneously at many points both on the top and bottom surfaces of the model for various wind directions. The local net pressure coefficients and the overall wind force and moment coefficients were computed by using the pressure data. The paper first describes the characteristics of the overall wind forces and moments acting on the roof with special attention to the load combination for discussing the design wind loads; the axial forces induced in the four imaginary columns at the roof corners are considered as the load effect for discussing the design wind loads. Then, the characteristics of the local net pressures are investigated. A brief discussion is made of the peak net pressure coefficients for cladding design.

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Characteristics of wind force on a double skin of building-high glazing façade were investigated by a wind tunnel test. The wind force on a double skin is affected remarkably by openings of the side-end of the skin. Pressure in a cavity between the outside and the inside skins becomes negative when wind attacks normal to the skin when the side-end are opened. Particularly, large negative pressure is induced in the cavity near the bottom opening by the accelerated flow, so the large positive net pressure acts on the outside skin where the peak pressure coefficient is 4.3, which is double of that on a single skin. When the side-end is closed and the openings are set at the top and the bottom of the outside skin, the pressure of the cavity is positive when wind attacks normal to the skin, so the peak net pressure on the outside skin is reduced to 70% of that on a single skin.

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The wind pressure on a building is intricately fluctuating with wind turbulence and vortex shedding. It is important to understand the characteristics of the pressure fluctuation for understanding the wind forces on a building. The POD ( Proper Orthogonal Decomposition ) analysis is known as a method of understanding multi-point fluctuation data. Already, the method is applied to the wind pressure of acting on a low-rise building or a square tall building. In this paper, the complexed POD analysis (variance matrix are expressed by complex number) are applied to the fluctuating pressure of an tall building. The other hand, the contribution of local pressure to the wind force of the whole model is calculated by the LRC ( Load Response Correlation) method.

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The authors have proposed a new type of greenhouse with a cross section similar to a wing. Such a cross section reduces the wind loads and realizes a long-span structure. Simultaneous pressure measurements were made with a scale model in a simulated turbulent boundary layer. First, the effects of wind speed and surface roughness of the model on the pressure distribution were investigated; several kinds of commercial sand paper were used for roughening the surface. Then, the design wind load for the main force resisting systems is discussed, based on three kinds of evaluation methods, i.e. a time-history response analysis, the LRC method and a gust effect factor approach. The results indicate that the gust effect factor approach gives a reasonable result for winds roughly normal to the ridgeline, while it results in a wind load distribution different from those predicted by the other two methods for oblique winds. The LRC method generally gives a result similar to that of the time-history response analysis. However, the result depends on the load effect under consideration. The value of peak factor is also dependent on the load effect; it is generally larger than 3.5. Finally, the peak pressure coefficients for cladding design are briefly discussed.

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The characteristics of the fluctuating external wind pressures on spherical domes have been investigated based on the data obtained from a series of wind-tunnel measurements in simulated atmospheric boundary layers. Focus is on the 1st to 4th moments of probability density function as well as on the power spectrum of pressure fluctuations. First, the effects of the roof geometry on these factors are discussed. Then, the dome surface is divided into two areas, i.e. Gaussian and non-Gaussian areas, according to the values of skewness and kurtosis. Finally, a model of the pressure field on the dome, that is, the mean and root-mean-square fluctuating pressure coefficients, power spectrum and so on, is proposed as a function of the rise/span and eaves-height/span ratios of the dome. This model is used for simulating the fluctuating wind pressures in the Gaussian and non-Gaussian areas. The simulated time history of pressure fluctuations can be used for fatigue analysis and risk consistent and more economical design.

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The dynamic characteristics of structures are often evaluated by measuring their vibrations. This is done to investigate wind vibrations of high-rise buildings or for other purposes. However, few vibration evaluations have focused on changes in the structural properties of buildings or on the rigidity of main structures and non-structural walls during construction. This paper describes changes of the dynamic characteristics of a high-rise steel chimney before and after setting a TMD during ambient conditions and strong wind. The damping ratios obtained by RD technique and FDD increase from 0.57% to 1.34% and from 0.71% to 1.45% after installing TMD, respectively. The damping ratio for ambient vibration is about 0.2% and is smaller than that during strong wind. This difference is caused from the difference of the amplitude of the acceleration between ambient response and wind-induced response.

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It is becoming increasingly important to carry out wind resistance design for base-isolated tall buildings. Otherwise, the wind-induced response of base-isolated building, using lead-plugged rubber bearings (LRB), predicted by the hysteresis model of an isolator for seismic response analysis has a large error, because the creep and re-crystallizations of LRB's lead portion caused by dynamic motion having static component. Therefore, a convenient method is proposed for estimating base-isolated-tall-building responses to strong winds, which comprise slowly- and quickly- varying components. This method proposed with considering of the experimental results for a LRB subjected to four types of ideal wind loads, show that the LRB brings one-side horizontal deformation with fluctuation, accompanied with creep and re-crystallizations of LRB's lead portion. And the last, comparing the dynamic tests results and the predicted results by the proposed method, the property of the proposed method is verified.

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Few researches on structural wind performance of buildings in timber-frame-construction have been conducted, in spite of being a popular kind of buildings in Japan. In this paper, a couple of statically cyclic loading experiments is carried out in order to obtain restoring force characteristics of two kinds of timber framed shear walls for evaluation of wind performance. The cyclic loading program is made in consideration of features of wind forces which contain mean values and continue for a long time. Next, the restoring force characteristics obtained by the experiments are modelized for time-historical response analyses. Although basic idea of modelization is based on combination of a normal bilinear model and a slip model, reduction of stiffness and energy absorption ability are also taken into consideration. Finally, influences of models on results of analyses are discussed.

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The accurate estimation of the unsteady wind force is necessary for the rational design of high rise buildings. For the accurate estimation of the unsteady wind force, it is necessary to evaluate the phase differences between the wind force and the response of structures. In such a case wavelet analysis with the complex wavelet is available. This paper presents the aerodynamic damping force and added mass on a square section prism with the aspect ratio of 5 evaluated by use of the wavelet analysis. The results are described for a field measurement with the large elastic model (1m×1m×5m). It is shown that the aerodynamic damping in the along wind direction is closely related with the oscillation amplitude and the structural damping.

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It is important to estimate the vibration characteristic of structures for the wind resistant design or the seismic design. Especially, the influence of the damping characteristic has on the vibration is large. In general, the Fourier analysis is used for the evaluation of the vibration characteristics. However, these methods are due to the statistical method based on the stationary stochastic process, and attention is required to apply to nonstationary phenomenon. Then, this paper proposes the technique for evaluating the work of external force, the increment of vibration energy and the dissipation of the structural energy from the generalization wind force and the building response by using the wavelet transform that is effective to handle nonstationary phenomenon. Moreover, this technique was applied to the field measurement result of using the square pillar elastic model, and the relation between the work of the wind force and the vibration energy was shown.

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Under approaching winds having non-stationary stochastic processes, the frequency domain analysis on gust responses is not practical and it is impossible to predict the maximum amplitude of the gust responses of structures. In order to overcome this underlying problem, a wavelet-based method to simulate gust responses is suggested. The time-scale characteristics present in wind fluctuations are configured with the system of the discrete wavelets and are reflected to the time histories of the gust responses to be synthesized. The time histories of the gust responses simulated with the proposed method are investigated specifically in respect to the peak factor.

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Wake excitation is an important problem for tandem circular cylinders. It is well known that this phenomenon is caused by the interaction between the downstream cylinder and the wake flow of the upstream cylinder. However, this phenomenon is affected by the Reynolds number because the flow properties around a circular cylinder are sensitive for this parameter. To simplify this phenomenon and investigate the only interaction between the downstream cylinder and the wake flow the Re-number effect should be reduced. In this study, some kinds of rectangular cylinders were used instead of the upstream circular cylinder to reduce the Re-number effects. It was aimed to understand the influence of the separation flow from the upstream rectangular cylinder on the aerodynamic response of the downstream circular cylinder, and to examine the excitation mechanism of the downstream circular cylinder. Two kinds of wind tunnel experiments were carried out as follows; Model response measurement with two degrees of freedom system and the surface pressure measurement of the downstream circular cylinder.

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Effectiveness of pulsating jet flows from inside of cylinder for suppression of wind-induced vibration is investigated by a series of specially arranged wind tunnel experiments. The jet flows are generated through thin slits along the two leading edges of a rectangular cylinder of d/b=2. The jet flows can be pulsated by two computer-controlled AC servomotor wind tunnels. Measured time histories of the cylinder displacements are immediately feed backed to the pulsating jets. The pulsating jets at the two leading edges always have the opposite phases. From the experiments, it is observed that the pulsating jet which has the same phase with the cylinder displacement is quite effective to suppress the vibration, whereas pulsating jets of different phases have less effect or even activate the vibration. The present experimental results suggest that the effective pulsating jet is perturbing the separated flow just when separation bubbles are being formed or start to grow. Interestingly, these experimental observations coincide to the preceding CFD results.

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This paper investigates the possibility of suppressing flow-induced vibration of a rectangular cylinder by applying periodic excitation to the flow around the cylinder. The excitation is applied at the leading edge of a rectangular cylinder through the sound by speakers. The characteristics of the vortex-induced vibration are examined through experiments. The experimental results show that the vibration amplitude of the cylinder was reduced significantly when there is a sound excitation with a specific frequency.

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Wake galloping and other vibrations were observed in the cables of the Hitsuishi-jima Bridge and Iwakuro-jima Bridge of the Honshu-Shikoku Bridges, and spacers and connecting wires were installed to control the vibration of the cables. However, the“Sub-Span Vibrationwith” with limited amplitude has been observed since the completion of the bridges, and it seems that this vibration causes the damage in the connecting wires. The application of the trip wires as the countermeasure to this “Sub-Span Vibration” was investigated. Wind tunnel tests with full scale sectional models and field tests were conducted and it was confirmed that the trip wires are effective. In this report, the results of the wind tunnel tests and field tests are reported.

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Wake-induced vibration (wake flutter) occurred at the twin hanger cables of the Akashi Kaikyo Bridge. Then, wind-tunnel study was carried out for twin cables with the cable distance of 4 – 11 times cable diameter. In this study, CFD analysis was made for twin cables in order to investigate wake-induced vibration. Based on the results of the flow characteristics around the cables and static force coefficients, comparison of characteristics of wake-induced vibration between the wind-tunnel test and the analysis was made. In addition, applying quasi-steady theory with the static force coefficients, the criterion formula of wake-induced vibration was examined.

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A new type of noise barrier with a fairing plate has been proposed to improve the aerodynamic stability of viaducts with noise barriers. However, such appendage is likely to lower the sound shielding efficiency. In this study, the sound shielding efficiency of the noise barrier with a fairing plate is examined through BEM. It is found that the sound shielding efficiency is higher, as the diffraction frequency is more abounding. The sound shielding efficiency is remarkably improved by the installation of sound absorbing materials to the upper surface of the fairing plate.

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This paper describes the fundamental aerodynamic characteristics of two edge girders, which have economical and structural advantages for future long span cable stayed bridges. Especially, for the purpose of the aerodynamic stabilization of two edge girders, the aerodynamic effects of the inclined lower flanges of two-edge girders are investigated by a series of wind tunnel tests, such as the measurement of unsteady aerodynamic forces and free vibration tests. In addition, the adaptable center span of cable stayed bridges with two edge girders is described. As one of conclusions, it was clarified that the geometrical girder shapes and the location of girders sensitively affect on the characteristics of the vortex-induced oscillation and the flutter instability of two edge girders, especially, the inclined lower flanges with two edge girders play an important role on characterizing the aerodynamic stabilization of two edge girders and assist the aerodynamic stability.

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Flutter Stabilization should be a major subject in long-span bridge design such as large strait crossing project. As a result of previous investigation on 2-box girder with a center air-gap in the two-dimensional model test supported with springs, it is indicated that flutter stability is improved by various attachment. However the influence of these attachments on aerodynamic characteristics has not been cleared enough. This paper aims to examine the influence of these attachment on aerodynamic characteristics of 2-box girder by unsteady pressure measurement.

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The cause of large horizontal response of a simplified cantilever bridge model in the wake of a conical hill was tried to be clarified. The fluctuating wind velocity and pressure as well as the bridge model response were measured simultaneously. The data were conditionally sampled based on the large horizontal response so that general fluctuating velocity and pressure characteristics that cause the response can be studied. Fluctuating wind velocity and pressure that cause the large horizontal responses are thought to act on the model along a line that is inclined about 40 degrees from perpendicular to the mean flow direction; this corresponds to previous response measurements and flow visualization results. Also the fluctuating pressure distribution with more uniform pattern was clarified to be dominant for the model with wind yaw angle of 40 degrees. Also possible flow pattern that causes the large response was implied by this study, but detail flow and pressure characteristics have to be clarified in further studies.

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When a steel pylon of cable-stayed bridge is standing alone before setting stay-cable, the pylon is susceptible to vibration under wind action. Especially the vibration of bridge axis tends to occur even in a lower wind velocity. The pylon of the Sakae-gawa Bridge was designed as the modified A-shaped one with rectangular cross sections, that is well known as one of sections unfavorable from aerodynamic aspects, and that, depending on side ratio, usually induces the vortex-excited vibration in lower wind velocity and galloping in higher wind velocity. Unfortunately, at the time requiring the aerodynamic investigation, there was no enough time to change the shape of cross section of the pylon. The authors tried to improve the aerodynamic characteristics by means of simple device attaching the vertical plates on the surface of the pylon, based on the separation interference method developed by Kubo. The effectiveness of the method is reported in the present paper.

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Stability of the quantile function estimation from the relatively short non-identically distributed data is investigated using large amount of fluctuating pressure measurement records acting on 3-D square section prism, which is exposed in a turbulent boundary layer. For the quantile function estimation, three kinds of frequently used methods, which are General Extreme Value distribution (GEVD), Type I distribution and General Pareto distribution (GPD) of declustered Peak Over Threshold (POT), and newly proposed translation method are considered. The investigation results clearly show that GEVD and a-priori assumed Type I (Gumbel) distribution are not appropriate for the estimation for large variance, and the results from GPD-POT method with declustering procedure show high possibility to underestimate quantiles compared with those derived from the large amount of independent block extremes. Among the considered methods, translation method shows the most stable estimation results with good accuracy.

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This paper describes a method for determining the universal wind load distribution that reproduces the maximum load effect on structural members. The method is applied to a cantilevered roof model to estimate the equivalent static wind load. The resonant component of the load effect cannot be ignored in the cantilevered roof. The equivalent static wind load for background components is estimated by using of the eigenvectors of wind force calculated by POD analysis. The equivalent static wind load for the resonant component is estimated by using equivalent static loads that reproduce the same shapes to the eigenvectors of the model. In addition to the mean, the background and the resonant component, the total equivalent static wind load can be estimated. The maximum load effects induced by the equivalent static wind load show good agreement with the true maximum load effects calculated by response analysis.

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In this paper, fluctuating surface pressure measurements are made for four flat roofed building models with square or rectangular plans in order to examine wind load combinations. The fluctuating pressures are integrated over all their surfaces and results are obtained as along-wind force, across-wind force, vertical force and torsional moment on their frames. The maximum wind force in consideration of the wind direction component and other simultaneously observed wind force components are examined, and some interesting facts regarding the wind force combinations are discussed on the basis of absolute value correlations, phase-plane expressions and so on. The maximum normal stresses in the column members of simple frame models are then examined in order to directly check the wind load combination effects.

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Scattering of roof tiles under strong wind is the most worrying problem in the wind engineering. A roof tile unbounded to the roof is significantly too light to prevent the scattering from the roof. In order to design a roof tile against strong wind, the appropriate wind coefficient of a roof tile should be decided. Wind force on roof tiles of an experimental house with a hipped roof was measured in natural wind. When wind attacks normal to the roof, peak wind forces of the roof tile were appeared. The value of maximum peak wind force coefficient was C_f =-5 on the edged roof and C_f =-3 on the general roof, respectively. The critical peak wind force coefficient of the roof tile was observed when the incline angle of the wind was vertical 10 degrees upward. The scattering wind velocity calculated using these coefficients is presumed approximately 10m/s, which is considered obviously too small compared with the design wind velocity of usual houses. Consequently, it is recommended that roof tiles are necessary to be fixed by somewhat binding method such as use a nail.

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The wind responses of a tower-supported steel stack are not well clarified for lack of the concerning full scale observation data, including both whole system of the stack itself and each truss member of the tower. This paper reports the long period field observation of a tower-supported steel stack at a Kyushu district. The observations were carried out using accelerometers, strain-meters and anemometers positioned at the stack. The observation results are as follows; 1) few dynamic responses of the stack itself were observed, 2) the large acceleration of some brace members due to vortex-induced vibration was observed, 3) the adjacent braces resonated each other, 4) each vibration mode of the adjacent braces was in opposite phase, 5) the larger the vibration acceleration of the brace is, the larger the magnitude of the opposite phase of the vibration modes contributed.

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One of the most important subjects in designing long-span bridges is to ensure aerodynamic stability of superstructure. In order to improve the aerodynamic stability, various researches were conducted and authors proposed a new type super-long span bridge which is excellent in economical efficiency and aerodynamic stability. This bridge has structural characteristics both of cable stayed bridge and suspension bridge. And the stiffening girder consists of slotted box girder part for the center of the main span to improve aerodynamic stability and standard 1-box girder part near the main towers to reduce construction cost of substructure. In this paper, main results of frame structural analysis and wind tunnel test of section model which were conducted in order to determine the structural dimensions of this new bridge with main span of 2.8km, are outlined first. Then the outline of design of 1/125 scale full model and the main results of the wind tunnel tests are described.

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The Tozaki Viaduct has a box girder with relatively low rigidity, and is located in the region of severe wind condition. Therefore, the lower skirt and double flap system was installed along with the Tozaki Viaduct as for the devices to aerodynamic stability. Because the devices were exposed themselves to the severe corrosive environment for more than 20 years corrosion on the devices gradually became problematic, and thus, the repair work would be considered unavoidable. On the other hand, the reduction of the maintenance cost has been focused on, and the necessity of the devices from the viewpoint of aerodynamic stability should be re-evaluated. Based on the structural characteristics and wind condition obtained after the completion of this bridge, the wind tunnel tests were conducted, and it was concluded that the double flaps and the lower skirts on the Tozaki peninsular side could be removed.

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